Firemen work as smoke billows from the windows of a mosque in the Swedish town of Eskilstuna, Thursday, Dec. 25, 2014. An arsonist set fire to the house of worship, injuring five people, police said. The incident comes amid an intense debate over immigration. Photo: Reuters/Pontus Stenberg/TT News Agency

An arsonist lit a mosque afire Thursday in Eskilstuna, an industrial city 86 miles west of the Swedish capital Stockholm, injuring five of the 15 to 20 people who were inside at the time. No suspect has been apprehended.

"A witness saw somebody throw an object through the window of the building, which serves as a mosque, after which a violent fire began," police spokesman Lars Franzell told Reuters. Images on local television showed flames and smoke billowing out of the house of worship.

Far-right parties with anti-Muslim agendas have increased in Europe in recent years, but until recently Sweden had been largely spared.

But the Sweden Democrats, an anti-immigrant populist party, shocked the country by capturing 13 percent of the vote in September’s general election that saw the country’s center-left coalition lose its majority. The 26-year-old party, which only broke into parliament in 2010, wants to curb immigrant asylum seekers by 90 percent.

Earlier this month, Sweden Democrats secretary Björn Söder raised concerns among liberal-minded Swedes when he said Jews, Sami (Laplanders) and Kurds should not be considered real Swedes until they assimilate into the country’s dominant culture, according to Financial Times.

This month, Stefan Löfven, prime minister since October, said the country will hold snap elections in March after the Sweden Democrats used their newfound power to vote against the country’s budget, forcing midterm elections for the first time in 50 years. There are an estimated 475,000 Muslim Swedes. About a fourth of them are active participants in the faith, many of whom are recent immigrants from the Middle East to the predominantly Lutheran country known for its liberal secular values.